Lubricating oils typically used in the industry comprise a mineral oil or synthetic oil as a base oil, and various additives for a particular purpose. Among various synthetic lubricants, polyalkylene glycols are unique because of their high oxygen content. These glycols have found use as petroleum lubricant replacements due to their unique attributes such as lower pour point, higher viscosity index, lower tendency to form tar and sludge, increased solvency, wider range of solubilities, higher flash points, lower vapor pressure, lower ash and metals content. The polyalkylene glycols that are used commercially as lubricants are homopolymers of propylene oxide which are water-insoluble, copolymers of ethylene oxide and propylene oxide which are water-soluble, polymers of butylene oxide, polymers of propylene oxide and higher epoxides, and polymers of propylene oxide that are dimethyl ethers. Polyalkylene glycol base stocks are available commercially, for example, from Dow under trade name “UCON Fluids”.
The polyalkylene glycols are generally prepared by ring opening polymerization of epoxides such as ethylene oxide, propylene oxide or butylene oxide with a starter that consists of an alcohol or diol and a smaller amount of its metal alkoxide, usually the potassium or sodium salt. The petrochemically derived ingredients used to manufacture polyalkylene glycols are, in general, toxic, highly flammable, volatile and thus are not safe, are difficult to handle and are not environmentally friendly. In addition, the polymerization reactions are highly exothermic and concentration of unreacted epoxides in the reactor can cause reactor failures.
Polytrimethylene ether glycol (“PO3G”) and its use have been described in a number of patents and patent applications. PO3G can be prepared by dehydration of 1,3-propanediol (PDO) or by ring opening polymerization of oxetane. PO3G can be prepared from 1,3-propanediol, preferably as described in U.S. Published Patent Application Nos. 2002/7043 A1 and 2002/10374 A1, both of which are incorporated herein by reference.
U.S. Published Patent Application No. 2002/7043 A1 teaches that the reaction mixture can comprise up to 50 mole %, preferably 1 to 20 mole %, based on all diols present, of a comonomer diol other than oligomers of 1,3-propanediol. Listed are 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 1,6-hexanediol, 1,8-octanediol, 1,10-decanediol, 1,12-dodecanediol and mixtures thereof. More preferred as comonomers are 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, and 2,2-diethyl-1,3-propanediol.
Similarly, U.S. Published Patent Application No. 2002/10374 A1 teaches that the reaction mixture can comprise up to 50 mole %, preferably 1 to 20 mole %, based on all diols present, of a comonomer diol other than oligomers of 1,3-propanediol. Listed are aliphatic diols, for example 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-dodecanediol, 3,3,4,4,5,5-hexafluro-1,5-pentanediol, 2,2,3,3,4,4,5,5-octafluoro-1,6-hexanediol, 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10-hexadecafluoro-1,12-dodecanediol, cycloaliphatic diols, for example 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol and isosorbide, polyhydroxy compounds, for example glycerol, trimethylolpropane, and pentaerythritol. A preferred group of comonomer diol is selected from the group consisting of 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 2-ethyl-2-(hydroxymethyl)-1,3-propanediol, 1,6-hexanediol, 1,8-octanediol, 1,10-decanediol, isosorbide, and mixtures thereof.
Synthetic lube oil compositions typically comprise a mixture of at least one synthetic base oil (base stock) and one or more additives. Depending on the application needs, a suitable base stock having desired properties can be selected and additives are employed for the purpose of improving the performance and properties of the base stock in its intended application.
By way of illustrative example, lubricating oils have been used to lubricate the bearings of positive displacement compressors, to seal the rotors, and to cool the compressed gases. Oxidation stability and varnish and deposit control are some of the important properties desirable in a lubricant for maximizing the life of the lubricant, and hence, the life of the equipment, especially under the high temperature and pressure conditions created when operating a positive displacement compressor, such as a reciprocating rotary vane, scroll, or rotary screw air compressor. It has also been desirable in the industry to provide a lubricating composition which does not deteriorate due to high temperatures. Thermal stability, demulsibility and hydrolytic stability, particularly under high temperature and pressure conditions of a lubricating oil are also desirable.
Polyalkylene glycols that are produced from ethylene oxide and propylene oxide have inherently low stability towards oxidation and thus require large amounts of an antioxidant that can cause undue lacquer formation on engine parts, due apparently to the stabilizer itself, and also increases the cost. U.S. Pat. No. 2,520,733, which is incorporated herein by reference in its entirety, discloses the use of poly(trimethylene glycol) as a lubricant which has better stability with or without antioxidants over propylene oxide polymers.
Gears are used in industry, transportation, and many other areas. Gears transmit power and alter the direction of movement. The load on gear teeth (the load-bearing surface) is intermittent and higher than on most other bearing or loaded surfaces. The lateral sliding action of gear teeth imposes severe lubrication requirements. While gear lubricants must have superior anti-wear and extreme pressure protection they must also be non-corrosive to “yellow metal” (copper alloy) components. Gear lubricants, particularly ones used in mining, milling, and similar operations need to be composed of high viscosity index oils and extreme pressure/anti-wear agents.
For water-soluble polyalkylene glycol as the base oil for lubricants encountering metal-to-metal contact under conditions of load or pressure, such as gear lubricants, it is necessary to increase wear resistance and improve extreme pressure properties. U.S. Pat. No. 5,342,531 which is incorporated herein by reference, describes the drawbacks of water-soluble polyalkylene glycols which include relatively poor solvency characteristics for most conventional antiwear and extreme pressure additives. Moreover, because polyalkylene glycols tend to be hygroscopic, excessive corrosion of metal surfaces can result under actual service conditions because of the presence of water picked up by the poyalkylene glycol base oil.
In compressor refrigerant systems, for example in automobile air conditioning systems, R134a (1,1,1,2-tetrafluoroethane) has been mentioned as a possible replacement for R12 (dichlorodifluoromethane) because of concern over potential depletion of the ozone layer. Unlike R-12, R134a is not miscible with mineral oils and consequently, different lubricants are required. If the lubricant separates from the refrigerant it would be expected that serious operating problems could result. For example, the compressor could be inadequately lubricated if refrigerant replaces the lubricant. Significant problems in other equipment could also result if a lubricant phase separates from the refrigerant during condensation, expansion or evaporation. Illustrative, non-limiting example of additives used with the lube oil base stock in compressor system applications are extreme pressure and antiwear additive, oxidation and thermal stability improver, corrosion inhibitor, viscosity index improver, pour point depressant, floc-point depressant, detergent, anti-foaming agent, viscosity adjuster and mixtures thereof.
According to U.S. Pat. No. 4,755,316, certain polyalkylene glycols having at least dual hydroxy functionality (that is, they are truly glycols, not esters or ethers) are particularly useful as lubricants with R134a. Polyoxypropylene glycols were found to be miscible with R134a over a satisfactory range. However, the hygroscopic nature of polyalkylene glycol could be an issue.
Also by way of illustrative example, lubricating oil compositions used to lubricate internal combustion engines contain base oil of lubricating viscosity, or a mixture of such oils, and additives used to improve the performance characteristics of the oil. For example, additives are used to improve detergency, reduce engine wear, provide stability against heat and oxidation, reduce oil consumption, inhibit corrosion, act as a dispersant, and reduce friction loss. Some additives provide multiple benefits, such as a dispersant/viscosity modifier.
To provide improved low temperature valve train wear performance, conventional lubricants are formulated with an antiwear additive. Metal hydrocarbyl dithiophosphates, particularly zinc dialkyldithiophosphates (ZDDP), are examples of an antiwear additive used in lubricating oils for internal combustion engines. ZDDP provides excellent wear protection at a comparatively low cost and also functions as an antioxidant.
Over the past several decades, the use of spark-ignited two-cycle (2-stroke) internal combustion engines has steadily increased. They are presently found in power lawn mowers and other power-operated garden equipment, power chain saws, pumps, electrical generators, marine outboard engines, snowmobiles, motorcycles and the like. The increasing use of two-cycle engines coupled with increasing severity of the conditions in which they have operated has led to an increased demand for oils to adequately lubricate such engines and to provide enhanced performance.
Grease lubrication of bearings, gears, and other components is used when seals or other devices can not be used to prevent migration of the lubricant away from lubricated surfaces. Grease consists of thickeners, typically 6 to 10 percent by weight of the mixture, lubricating oil, and additives to enhance the performance of the grease. The thickener in grease acts as a “sponge” to keep the oil and additives on the bearing, gear, or other component being lubricated. The additives used in grease blending are similar to the ones used in the production of gear, engine oil, and other petroleum-based lubricants.
Upper cylinder lubricants act to lubricate and clean the ring and upper cylinder area of spark and compression ignition engines. This action can benefit fuel economy, emissions, as well as ring and cylinder wear.
With the development of disk brakes, more powerful engines and heavier vehicles, brake fluids with increasing thermal stability are required.
In hydraulic systems for motor vehicles auxiliary aggregates operated with piston pumps or vane pumps are used to an increasing extent (for example, steering and coupling aids, antiblocking devices, level regulators). Consequently, higher demands are made on the lubricating properties of the hydraulic fluid. Hydraulic fluids used in automotive hydraulic brake systems must satisfy a variety of requirements. In general, these include chemical and thermal stability, suitable viscosities for the intended use, fluidity over the use-temperature range, low volatility, non-corrosiveness to metals, limited effect on rubber parts and good tolerance for water. Thus, a hydraulic brake fluid to be commercially acceptable is required to meet industry-accepted specifications as well as those established by governmental agencies.